Learn Hardcore Indonesian: Dokter menjelaskan bahwa kafein dan layar terang punya efek besar pada kualitas tidur. - The doctor explained that caffeine and bright screens have a big effect on sleep quality.

In formal or careful written Indonesian, bahwa is common and sounds natural.
In everyday spoken Indonesian, people often drop it, especially after verbs like bilang (to say), kata (said), anggap (to consider), etc.

In your sentence:

Dokter menjelaskan bahwa kafein dan layar terang punya efek besar pada kualitas tidur.
You might also hear (slightly more casual):
Dokter menjelaskan kafein dan layar terang punya efek besar pada kualitas tidur.

Both are understandable, but the version with bahwa is clearer and more standard, especially in writing or formal speech.

Why is punya used here instead of something like memiliki or mempunyai? Is punya informal?

Punya literally means “to have” or “to possess”. In this sentence it is used in a broader, more abstract way:

kafein dan layar terang punya efek besar
→ caffeine and bright screens have a big effect

About formality:

punya is neutral–informal and very common in speech and in informal writing.
memiliki and mempunyai are more formal and often used in written or official contexts.

You could also say:

kafein dan layar terang memiliki efek besar pada kualitas tidur.
kafein dan layar terang mempunyai efek besar pada kualitas tidur.

These are grammatically correct and sound more formal or bookish.
The original with punya sounds natural in everyday conversation or neutral text.

Can punya really be used with non-human things like kafein and layar terang?

Yes. In modern Indonesian, punya is widely used with non-human or abstract subjects, not only with people.

Examples:

Kopi punya aroma yang kuat.
→ Coffee has a strong aroma.
Kota ini punya sejarah panjang.
→ This city has a long history.
Kebiasaan begadang punya dampak buruk pada kesehatan.
→ The habit of staying up late has a bad impact on health.

So kafein dan layar terang punya efek besar is perfectly natural.

Why is it layar terang and not terang layar? What is the usual word order with adjectives?

In Indonesian, the normal order is:

NOUN + ADJECTIVE

So:

layar terang = bright screen (literally “screen bright”)
kualitas tidur = sleep quality (here, kualitas is the main noun; tidur describes what kind of quality)

You do not usually say terang layar in standard Indonesian. That order is wrong for a noun phrase.

More examples:

rumah besar = big house
jalan panjang = long road
makanan sehat = healthy food

So layar terang follows the normal pattern: noun (layar) + adjective (terang).

Could we say layar yang terang instead of layar terang? Is there any difference?

Yes, you can say layar yang terang, but it has a slightly different feel.

layar terang = a general or typical bright screen (neutral description)
layar yang terang = the screen that is bright / a screen which is bright, with more emphasis or specification

In your sentence:

kafein dan layar terang punya efek besar …
sounds like a general statement: caffeine and bright screens (in general) have a big effect…

If you say:

kafein dan layar yang terang punya efek besar …
it can sound more like you are contrasting bright screens vs non-bright screens, or pointing to a more specific characteristic.

Both are grammatical; layar terang is more compact and typical for a general statement.

What is the difference between efek and pengaruh? Could we say punya pengaruh besar instead?

Both efek and pengaruh can mean “effect / influence”, but they have slightly different nuances:

efek
- often closer to “effect” in a somewhat scientific / technical sense
- used a lot in contexts like efek samping (side effect), efek obat (drug effect)
pengaruh
- closer to “influence, impact”
- slightly broader and often used in social or psychological contexts

You can definitely say:

kafein dan layar terang punya pengaruh besar pada kualitas tidur.

This is natural and common.
The sentence with efek might feel a bit more clinical or scientific, but both are very acceptable here.

Why is it pada kualitas tidur? Could we also say terhadap kualitas tidur or untuk kualitas tidur?

All three are possible, but they have different typical uses:

pada kualitas tidur
- very common after words like efek, pengaruh
- can often be translated as “on” or “to”
- sounds natural and standard here
  → punya efek besar pada kualitas tidur = “have a big effect on sleep quality”
terhadap kualitas tidur
- slightly more formal
- also common with efek, pengaruh, sikap, etc.
  → punya efek besar terhadap kualitas tidur = also “have a big effect on sleep quality”
untuk kualitas tidur
- more like “for sleep quality” (for its benefit or purpose)
- used more when talking about things that are good/bad for something
  Example: Kebiasaan ini buruk untuk kualitas tidur. = This habit is bad for sleep quality.

In your exact sentence, pada and terhadap are the most typical choices; pada is slightly more neutral and common in speech.

There is no word for “the” or “a” before dokter. How do we know if it means “the doctor” or “a doctor”?

Indonesian has no articles like “a/an” or “the”. The noun dokter on its own can be translated as either:

a doctor
the doctor

The exact English translation depends on context:

If we already know which doctor, or there is only one relevant doctor in the situation, we translate as “the doctor”.
If the sentence is introducing a previously unknown doctor, we might translate as “a doctor”.

The Indonesian sentence itself does not mark this difference; it’s inferred from context.

The verb menjelaskan looks like a past tense in English (“explained”), but Indonesian doesn’t mark tense. Could this also mean “explains” or “is explaining”?

Indonesian verbs generally do not change form for tense (past, present, future).

Menjelaskan only indicates “to explain” (an action), without inherent tense. The time is understood from:

context, or
additional time words like tadi (earlier), kemarin (yesterday), sedang (in the middle of), etc.

So Dokter menjelaskan bahwa … can mean:

The doctor explained that … (past)
The doctor explains that … (present, general)
The doctor is explaining that … (present progressive, with the right context)

If you want to emphasize it is happening now, you can add sedang:

Dokter sedang menjelaskan bahwa … = The doctor is explaining that …

But the base menjelaskan itself is tense-neutral.

What is the difference between menjelaskan, mengatakan, and bilang?

All three involve speech, but with different focuses and levels of formality:

menjelaskan
- means “to explain”
- focuses on clarifying, giving explanation or details
- relatively formal / neutral
mengatakan
- means “to say, to state”
- more formal than bilang, common in writing and news
- Dokter mengatakan bahwa … = The doctor said that …
bilang
- everyday, informal word for “to say”
- often used in casual conversation
- Dokter bilang kafein punya efek besar … = The doctor said caffeine has a big effect …

In your sentence, menjelaskan is good because the doctor is not just saying something, but explaining a cause-and-effect relationship.

Is kafein just the Indonesian spelling of “caffeine”? Are there other words for it?

Yes. Kafein is the standard Indonesian spelling that corresponds to English “caffeine”.

Pronunciation roughly: ka-fe-in (3 syllables)
It is widely understood in everyday speech, media, and scientific contexts.

There are no common alternative everyday words; you might occasionally see the English spelling caffeine in marketing or technical texts, but kafein is the normal Indonesian form.

How formal or casual is this whole sentence? Would it sound natural in a doctor–patient conversation?

The sentence is neutral in formality and would sound natural both in spoken and written contexts:

Dokter – neutral
menjelaskan – neutral/formal verb, but common
bahwa – slightly formal, but okay in speech
punya – leans informal/neutral, balances the formality of menjelaskan and bahwa
efek besar pada kualitas tidur – normal, slightly scientific/medical style but very common

A doctor talking to a patient could definitely say this sentence (perhaps with a slightly simpler or more conversational variation), and it would not sound odd.

Why is it efek besar and not efek tinggi? When do we use besar versus tinggi?

Both besar and tinggi can be translated as “big/high”, but they are used differently:

besar is used for size, degree, or magnitude in a broad sense:
- risiko besar = big risk
- pengaruh besar = big influence
- efek besar = large effect
tinggi is used for height, level, or measurement:
- suhu tinggi = high temperature
- tekanan darah tinggi = high blood pressure
- kadar kafein tinggi = high caffeine level

Because we’re talking about the magnitude of the effect, efek besar is the natural choice, not efek tinggi.